🎓 Learn

Sixteen written modules — 34,469 words — covering the protocols, records and attacks behind every tool on this site. Each one explains the mechanism, works through a real example, names the common failure modes, and links to the live tool that shows you the same thing against a target of your choosing. Free, no signup, no account.

Networking & DNS

📦How the Internet Actually Moves a Packet

Read a packet capture and know what every layer added. Explain the TCP handshake, MTU and fragmentation, NAT, and exactly what happens between pressing Enter on a URL and seeing a page.

~12 minBeginner

🧮Subnetting and CIDR Without the Pain

Split a network in your head. Prefix lengths, network and broadcast arithmetic, a full worked /24 → four /26s example, the reserved ranges worth memorising, and why IPv6 subnetting is easier.

~11 minBeginner

📖DNS: Resolution, Records and How It Gets Attacked

Follow a query from stub resolver to authoritative server, write every common record type by hand, and understand cache poisoning, subdomain takeover, zone transfers and DNS exfiltration.

~14 minIntermediate

🌍Routing, ASNs and BGP

Understand the internet as a network of networks: autonomous systems, transit versus peering, anycast, how a BGP path is chosen — and what route hijacks, RPKI and ROAs actually mean.

~13 minIntermediate

Web Application Security

📋HTTP Security Headers, Explained Header by Header

Read and write every header that matters — HSTS, CSP, nosniff, Referrer-Policy, Permissions-Policy, the cross-origin trio — and know precisely what each one does not protect. Ends with a baseline set you can paste.

~14 minBeginner

🔟The OWASP Top 10, With Real Examples

Walk the 2025 edition category by category with a minimal concrete example of each flaw and the specific control that fixes it — plus a 2021 → 2025 mapping table, because the old list is still quoted across compliance paperwork and tooling.

~16 minBeginner

💉Injection Classes: SQLi, XSS, SSRF, Traversal and Friends

One idea explains all of them: data crossing into a control channel. Learn the mechanism behind each class and the fix that actually holds, instead of the escaping folklore that does not.

~15 minIntermediate

🍪Cookies, Sessions and Authentication

Cookie attributes in full, session fixation, JWT pitfalls, OAuth with PKCE, password hashing parameters that are current, and why phishing resistance is the only MFA property that really matters.

~15 minIntermediate

Cryptography, TLS & Email

🔑Cryptography You Actually Need to Know

Pick the right primitive and the right mode, understand why a repeated nonce is fatal, and know exactly what "MD5 is broken" does and does not mean.

~14 minBeginner

📜TLS and the Certificate Chain of Trust

Read a handshake, decode a cipher suite, follow a chain from leaf to root, and diagnose the six failures that cause almost every real TLS incident.

~15 minIntermediate

✉️Email Authentication: SPF, DKIM, DMARC and Beyond

Write correct SPF, DKIM and DMARC records, understand alignment, and roll a domain from p=none to p=reject without losing legitimate mail.

~15 minIntermediate

🧮Passwords, Hashing and Credential Attacks

How credentials are really stolen, how to store them so a database dump is survivable, and what genuinely replaces the password.

~14 minBeginner

Recon, Defence & Ethics

🛰️Reconnaissance Methodology

Learn exactly where the line sits between passive and active recon, then follow a repeatable order of operations that turns scattered lookups into a real attack-surface inventory.

~12 minIntermediate

📡Logging, Detection & MITRE ATT&CK

Decide what to log and what each source is worth, write detections that survive contact with reality, and use ATT&CK for coverage mapping instead of decoration.

~14 minIntermediate

🧱Hardening That Is Worth Doing

Prioritised, copy-pasteable checklists for a Linux host, a web application, DNS and email, and cloud — with the reasoning for every line and the tool here that verifies it.

~15 minIntermediate

⚖️Authorisation, Ethics & Disclosure

What written authorisation actually contains, how coordinated disclosure works, what to do when you find personal data, and why the technique alone never makes you the good guy.

~14 minBeginner

Every module is written to be read on its own, but they build in order within a track. When you want to test what you have just read, the toolkit runs the same checks live, and the reference tables hold the lookups.